Phase Shifters are devices, in which the phase of an electromagnetic wave of a given frequency can be shifted when propagating through a transmission line. In many fields of electronics, it is often necessary to change the phase of signals. RF, microwave, and millimeter-wave (mm wave) phase shifters have many applications in various equipment, such as, for example, phase discriminators, beam forming networks, IQ vector modulators, power dividers, linearization of power amplifiers, and phased array antennas.
FIG. 1 shows one type of prior art RF phase shifter, called a reflective phase shifter (100), which uses a hybrid coupler (110), for example, a Lange coupler as known to a person skilled in the art, and a pair of reflective terminating circuits (135) coupled to a pair of ports, labelled as Coupled Port and Direct Port, of the hybrid coupler (110). The hybrid coupler (110) splits an input signal provided at an input port, Input Port, into two signals of equal power but ninety degrees, 90°, out of phase that are provided at the Coupled Port and the Direct Port. Accordingly, these signals reflect from the pair of reflecting terminating circuits (135), and combine in phase (constructively) at the phase shifter output, labelled as Isolated Port, so long as the pair of reflective terminating circuits (135) are identical in reflection coefficient (both magnitude and phase).
In some cases, as shown in FIG. 1, the pair of reflecting terminating circuits (135) can be switchable loads, to provide, for example, different phase shifts between an input RF signal at the input port, Input Port, and a shifted version of the input RF signal at the output port, Isolated Port. Switching of the loads can be provided via a pair of switches, S1, S2, which can be, for example, FET switches.
As shown in FIG. 1, the pair of reflective terminating circuits (135), each comprise reactive elements, arranged as two separate reactive loads (e.g. (L1, C1) and (L2, C2)), which are configured to provide the different phase shifts. In the exemplary case depicted in FIG. 1, when switch S1 is closed and switch S2 is open, the reactive load (L1, C1) is coupled to the Coupled Port and the Direct Port, and a phase, Phase(S1), which can be considered as a reference phase at a particular frequency, is provided at the output port, Isolated Port. On the other hand, when switch S2 is closed and switch S1 is open, the reactive load (L2, C2) is coupled to the Coupled Port and the Direct Port, and a phase, Phase(S2), at the particular frequency, is provided at the output port, Isolated port, where a relationship between the two phases, Phase(S1) and Phase(S2), is such that a phase shift, ΔΦ=Phase(S1)−Phase(S2), is approximately equal to one hundred and eighty degrees (ΔΦ=180°) at the particular frequency. A person skilled in the art would know that in the configuration depicted in FIG. 1, the phase, Phase(S1), is considered as a reference phase. More description on such configuration, including optimization of the reactive loads for a reduced phase error of the provided phase shift, ΔΦ, can be found, for example, in the above sited reference, U.S. Patent Publication No. 2017/0194688 A1, the disclosure of which is incorporated herein by reference in its entirety.
A constant need for higher frequencies of operation of the reflective phase shifter (100) of FIG. 1 (e.g. mm wave; 30 GHz-300 GHz) may in turn push component values of the reactive loads (e.g. (L1, C1), (L2, C2)) to impractically small values. This coupled with an inherently higher insertion loss (IL), about 3 dB and higher, as well as a relatively high physical layout size, of the reflective phase shifter (100), is a motivation for the teachings according to the present disclosure.